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April 23, 2009

China’s Shrinking Forests Absorbing Less CO2

by Sam Savage

In the latter half of the 20th century, the lush vegetation of China's forests and grasslands was absorbing roughly one third of the country's greenhouse gas emissions. According to a recent study, however, that rate is declining rapidly.

Peking University researchers say that a combination of factors including high rainfall, government programs to replant forests, shifts in crop use and a higher concentration of bamboo biomass have all played a part in absorbing some 28 to 37 percent of industrial carbon dioxide emissions between 1980 and 2000.

The new study was the first of its kind since China recently topped the U.S. as the world's largest emitter of greenhouse gases. Researchers attempted to obtain a more exact picture of the role that plants play in offsetting the carbon dioxide released by industrial activities.

During the process of photosynthesis, in which plants harness the sun's energy to produce sugar molecules, they extract CO2 from the air to use as the backbone of glucose molecules, while at the same time releasing the unneeded oxygen molecules back into the environment.

The study, published in this month's edition of the scientific journal Nature, also made mention of the fact that China's vegetation absorbs more carbon dioxide per square meter than Europe's greenery but less that the United States.

U.S. scientists blame China's growing carbon dioxide absorption deficit on China's rapidly expanding industrial sector, which in recent years has been growing exponentially faster than the country's vegetation.

"It's dropping like a rock," says Kevin Robert Gurney of Purdue University on China's declining carbon dioxide absorption balance.

In 2007, China's vegetation was only able to absorb some 10 to 15 percent of their industrial carbon dioxide emissions "“ a third of what they were capable of taking in during the peak years in the 1980's.

According to the International Energy Agency (IEA), forecasts show that these rates will continue to fall, being halved again to 6 to 8 percent by the year 2030

U.N. officials report that in the last year China has been opening new coal-fueled power plants at a rate of more than one a week at the same time many western governments are attempting to pass legislation to curb the growth of new coal-powered facilities.

Worldwide, scientists estimate that plants absorb between 10 to 60 percent of human-emitted carbon dioxide. The global scale of plant-mediated gas exchange is so large that scientists are able to measure seasonal fluctuations in the atmospheric content of carbon dioxide and oxygen as many plants lose their leaves and stop photosynthesizing for the winter.

The Chinese report also mentioned that as demographics shift and people move to the cities less firewood and charcoal are being burned in the countryside; a decrease in carbon dioxide emissions that will more than likely be offset by an increased consumption of fossil fuels.

Gurney says the report has offered other researchers around the world a welcome insight into China's emissions situation. "We haven't had a really good handle on the Chinese emissions until now," he commented.

In keeping with a new U.N. climate treaty, more the 190 countries have agreed to attempt to slow deforestation. Successful countries will earn credits for passing appropriate legislation, though Gurney says that China will be able to claim only a few credits for a handful of deliberate reforestation projects.

The U.N. Climate Panel has officially stated that greenhouse gases are at least partly to blame for the planet's rising temperatures which are expected to bring an increase in disturbing weather patterns and natural disasters in the years to come.